1. Field of the Invention
The present invention relates to inspecting fuel channels and more particularly to generating a flatness profile of a measured channel.
2. General Background
Boiling water reactor (BWR) fuel channels are routinely disposed of prematurely because a small percentage of these channels warp (bow and bulge) to the extent that the control grid spacers between the channels bind against the channel walls and cannot be inserted or withdrawn. Current methods for inspecting these channels requires placing the fuel assembly in a fixture and moving sensors, either linear variable displacement transformers (LVDT), eddy current, or ultrasonic transducers (UT), along the face. A numerical indication of the flatness of the channel is generated by measuring the distance from a physically flat or mechanically corrected flat reference plane to the channel surface. This technique requires a large rigid structure to minimize errors from flexure and to support the moving transport on which the sensors are mounted. The polar crane used to move the channels to the measurement fixture must be disconnected to minimize vibration and associated measurement error. In addition, the large number of mechanical moving parts in such an arrangement are subject to excessive wear and failure rates. Flatness measuring devices known in the art include the following.
U.S. Pat. No. 3,875,667 entitled "In-Line Straightness Sensing Device" issued to Wilke discloses a device for sensing the straightness of a running length of rod or wire wherein a pair of sensors are disposed perpendicularly to each other adjacent the rod whereby deviations along the X--X and Y--Y axis of the rod are sensed, the sensors being connected to a readout device for displaying the sensed deviations.
U.S. Pat. No. 4,048,009 entitled "Method Of and Apparatus For Checking The Dimensions of the Extensions Of The Control Rods Of A Nuclear Reactor" issued to Weilbacher discloses a method of checking the dimensions of the extensions of control rods wherein measuring sensors arranged in accordance with the profiles of the extensions and calibrated by reference to the support move along the extension and measure the distance between the sensors and the extension at a plurality of levels.
U.S. Pat. Nos. 3,511,091 entitled "Device For Monitoring Parallel Tubular Elements", 3,596,362 entitled "Surface Measuring Apparatus", 3,621,580 entitled "Machine For The Dimensional Control Of Elements For Nuclear Fuels", 3,664,922 entitled "InService Inspection Of Reactor Vessel Welds", 3,724,084 entitled "Alignment Apparatus", 4,574,494 entitled "Device For Determning The Profile Of The Charging Surface Of A Shaft Furnance", 4,577,497 entitled "Apparatus And Method For Measuring The Wear Of Railroad Rail", 4,583,294 entitled "Position Sensing Apparatus", and 4,598,483 entitled "Apparatus And Method For Verification Of Jacket For Floppy Disks" disclose methods and systems for dimensional measurement and are representative of the known art.
U.S. Pat. No. 4,048,009 to Weilbacher is similar to the measuring systems presently in use. The control rod drives are anchored top and bottom to a rigid fixture. Sensors are then moved along a vertically or horizontally oriented structure to calibrate the sensors and travel mechanism. The sensors are then moved along the rod to measure the surface profile.
U.S. Pat. No. 3,875,667 to Wilke only measures the flatness of the rod or wire as a displacement of a center contact with respect to two additional contact points. A single number is displayed.
The patents do not provide solutions to existing problems in the art. Weilbacher requires the use of a large bulky structure with a long flatness reference which must be mechanically corrected and calibrated while Wilke provides only a single reference number to indicate displacement. Neither system incorporates the axial position and displacement to develop a contour profile of the item being measured.